The invention relates to a method for machining the flanks of gears by skiving, and to apparatus for implementing such method.
For some years, the market has increasingly been demanding methods according to which gears in the hardened condition can be finish machined. This also applies to cylindrical gears which are used in large-scale production, for example, in automobile construction. On one hand, the demand is based on the desire to transmit higher outputs than previously in the case of smaller construction volume of gearing with the lowest possible noise generation, and on the other hand due to the knowledge that the hardening process is still not sufficiently controllable, so that, for example, gears which have had a very high tooth quality before hardening, frequently have inadmissibly high geometrical deviations (errors) after hardening.
The methods used in the past in large-scale production for machining tooth flanks after hardening do not yet meet the requirements of the market. The methods are in particular either too slow and therefore too expensive, or the gearing quality which can be achieved leaves something to be desired.
Based on these findings, a series of new or at least improved methods for machining the flanks of hardened cylindrical gears have been developed in the past several years. Among these methods are skive hobbing with specially designed carbide hobs; grinding with a globoidal grinding worm which is profiled, for example, via a diamond-coated dressing gear; form grinding with a CBN-coated form-grinding wheel by a single indexing method; grinding with a gear-shaped tool which in practice is designated as honing; fine finishing or hard shaving, or grinding with a CBN-coated grinding worm.
Each of these methods still has serious disadvantages for application in mass production. The main criteria for application in mass production are high geometrical quality and superior surface finish; a high rate of metal removal, that is, a high chip removing rate; low machining costs; low tool maintenance requirements, and a simple resetting of the machine. Moreover, it must be possible to machine with the method gears which, apart from the gearing to be machined, have an axially offset collar or a second gearing, sometimes only a small intermediate space being present between the gearing and axially offset collar or the second gearing. It must also be possible to machine internal gearings with the method.
Skiving is known for machining cylindrical gears. This machining method has two main features. On the one hand it permits a high tooth production rate und thus a short machining time; on the other hand, it can only produce gearings in coarse quality. All attempts to produce high quality gearings by skiving have failed. Thus, for example, the production of a machine specifically developed in the United States for the finish machining of unhardened, externally toothed cylindrical gears by skiving has been stopped.